The present invention is related to digital image processing, and more particularly, digital still camera or digital video camera systems which employ a single image sensor with a color filter array.
In electronic color image systems, each image consists of a two-dimensional array of pixels and the full color of each pixel is represented by three color planes, usually red (R), green (G) and blue (B). Image light from a subject is converted to electric signals by a two dimensional array of photo-detectors, i.e., image sensor. To capture the information of the each color plane, three image sensors are used to detect light intensity of each color. But sometimes only one image sensor covered by a two-dimensional mosaic color filter array (CFA) is used for reducing cost, miniaturizing system, etc. The Bayer pattern is one of the commonly-used mosaic patterns for the CFA. FIG. 2a shows how red, green and blue filters are configured in the Bayer pattern. Gr is the green when the horizontal neighbor is red; and Gb is the green when the horizontal neighbor is blue.
In a system employing a CFA (e.g., FIG. 2d image pipeline for a digital camera), only one color data is obtained at each pixel site, though thee color values (R, G, and B in the Bayer case) at each pixel site are needed to represent the color of the subject. Then reproduction of the other missing colors from existing color data, i.e., demosaicing process, is required. But simply averaging neighboring colors to interpolate missing colors causes faulty colors at subject edges, et cetera. Much work has been performed to solve the problem (e.g., U.S. Pat. No. 5,506,619) but the results are unsatisfactory. Therefore, a good interpolation method is still lacking for high quality images.